1. Field of the Invention
The invention relates to electrocardiology, and more particularly to electrocardiographic (ECG) scanning.
2. Description of the Prior Art
The term xe2x80x9cECG leadxe2x80x9d is used here to denote a vector at the ends of which a potential difference reflecting electric signals of the heart is sensed. An electrocardiogram (an ECG) is a tracing recorded in an ECG lead. The terms xe2x80x9csynthesized leadxe2x80x9d and xe2x80x9cscanning leadxe2x80x9d are used here interchangeably.
It is known that the collinearity of electrophysiologic activity of the heart with the direction of an ECG lead results in a most manifesting ECG pattern. It is an established practice to utilize fixed leads (such as 12 standard ECG, vectorcardiographic (VCG), body surface potential mapping (BSPM), or other lead sets) for ECG diagnosis. However, the collinearity cannot be always achieved with fixed leads, even with numerous BSPM leads. Pathological signs that are non-collinear with directions of the conventional leads do not always reach diagnostic thresholds and may be missed.
Positions of electrodes of the conventional ECG leads reflect historic preferences, convenience of electrodes placement, and proximity to the heart (and hence higher voltages) rather than the necessity to representatively demonstrate cardiac sources of electric potentials. Indeed, the unipolar chest leads are located almost in the same plane within one third of the circumference, scalar VCG presents electric signals of the heart as being projected on just three orthogonal leads, and BSPM does not show potential distribution at the top and bottom of the torso.
In the conventional electrocardiography propagation of electric signals of the heart to sensing electrodes is affected by extracardiac factors of different magnitude, which results in distorted propagation ways and variable impedance making voltages in different leads difficult to compare and analyze and requiring application of different voltage norms for the same parameter in different leads (e.g., different normal values for R-amplitudes or ST-deviation in chest and limb leads that reflect the same regions of the myocardium).
The indicated problems of utilizing ECG leads collinear with pathological changes, increasing the spatial coverage of ECG leads, and getting tracings of comparable voltages have been partially solved by a manual ECG scanner disclosed in the Russian patent #2077865 to Tereschouk. It has been shown that ECG diagnosis could be more accurate if ECGs are recorded in all directions. The patent discloses a manual ECG scanner that includes electrodes on a patient for sensing electric signals of the heart, synthesizer of three orthogonal leads from original leads sensed on a patient, synthesizer of ECG leads having arbitrary positions from the orthogonal leads, and an electrocardiograph. The synthesizer of ECG leads includes three channels. Each of the channels includes preamplifier, potentiometer, and phase inverter enabling arbitrariness of contributions of the three orthogonal leads, and hence arbitrariness of the position of a synthesized ECG lead.
By comparison with BSPM, an ECG scanner does not need a hundred of channels (and associated electrodes, wires, amplifiers, etc.) while it generates an unlimited number of leads embracing the whole three-dimensional space (including the top and bottom of the torso to observe inferior and basal segments of the myocardium) and is easier to perform and interpret. As opposed to the standard 12-lead ECG, an ECG scanner generates omnidirectional ECG leads producing tracings that are easier to analyze as they have comparable voltages. As distinct from VCG, which remains unpopular mainly due the intricacy of its interpretation, ECG scanning demonstrates electric signals of the heart specific for each spatial position of a scanning lead and presents results in a traditional scalar form without requiring extra training for physicians.
The manual ECG scanner of the prior art is useful for validating the new diagnostic principle of scanning the three-dimensional space to identify ECG leads exhibiting diagnostically significant signs and training in electrocardiology. However using three potentiometers in ECG scanning is confusing, time-consuming, and inconvenient. Thus an object of the present invention is to provide with an easy-to-use manipulator for a manual ECG scanning.
Manually ECG scanning is insufficiently accurate and effective, and thus hardly appropriate for the contemporary healthcare environment. The goal of this invention is to create an automated comprehensive ECG scanning system that could become a clinical routine.
In manually scanning of the prior art ECG leads are synthesized at irregular spatial and temporal intervals while the electric activity of the heart is different at different locations and changes over time making results of the prior art ECG scanning inaccurate, incomplete, and irreproducible. For example, a sign of myocardial infarction might be missed in a non-systematic ECG scanning, inasmuch as none of the synthesized ECG leads is collinear with that sign. In fluctuating cardiac pathology (dysrhythmia, conduction disorders) or deep breathing the temporal dissociation in synthesizing a number of ECG leads results in tracings reflecting absolutely different states of the heart that are impossible to analyze for the purposes of ECG scanning.
Therefore an object of this invention is to create an instrument for automatically and systematically synthesizing an array of ECG leads composing the three-dimensional space in a predetermined order to prevent information loss. Another object of the invention is to develop a method for automatically and systematically analyzing signals in an orderly-synthesized array of ECG leads to detect pathology in a lead that is collinear with a pathological sign.
Furthermore, an object of this invention is to make the process of ECG scanning controllable by an investigator, including building a means for selecting scanning parameters, such as diagnostic criteria.
The prior art does not recognize that parameters of ECG scanning should be adjusted for patients"" electrophysiological variability. Therefore an object of this invention is to improve accuracy and reproducibility of ECG scanning by creating an automated learning system for adjusting parameters of combining ECG leads for a particular patient.
Another object of this invention is to make information about the three-dimensional position of a synthesized ECG lead readily available to an investigator.
Finally, an object of the current invention is to build a cardiac imaging system that would match changes in a patient""s cardiac morphology and electrophysiology.
Electrocardiographic (ECG) scanner is a system for electrocardiological diagnostics by combining original ECG leads having known spatial positions into synthesized ECG leads having arbitrary spatial positions, analyzing electric signals of synthesized ECG leads, and producing scalar tracings (synthesized ECGs) in them. This invention improves manually ECG scanning of the prior art, and discloses automated ECG scanning.
It has been found that manually ECG scanning could be conducted more conveniently and effectively utilizing a three-dimensional rotating ball-type manipulator. A manipulator has three orthogonal sensors to set shares of the three respective orthogonal leads in a synthesized ECG lead. Each position of the ball of a manipulator corresponds to a fixed combination of shares of orthogonal leads determining a unique spatial position of a synthesized ECG lead. The ball is graduated to show to the investigator the spatial position of a synthesized lead. In a preferred embodiment the manipulator is a three-dimensional trackball, and its housing has an opening at about the equator of the rotating ball to ease manual rotation of the ball around its vertical axis through that opening.
It has been discovered that ECG scanning could be executed automatically providing with more comprehensive, accurate, and readily analyzable results if an ECG scanner included a means for systematically combining original ECG leads with known spatial positions into an array of synthesized ECG leads with arbitrary spatial positions. A means for combining ECG leads includes a means for calculating in a predetermined order shares of original leads in synthesized leads; a means for acquiring and combining synchronous electric signals of original leads in accordance with the calculated shares; and a means for computing positions of synthesized leads.
Furthermore, it has been found that a means for controlling parameters of combining ECG leads was fundamental for managing automatically scanning by an investigator and producing reliable and accurate scanning results. A means for controlling parameters of combining regulates spatial (constants, functions, independent variables and a range of their variations as determined by scanning pattern, step, and sector) and temporal (scanning time, period, rate) parameters of combining ECG leads. A scanning pattern is the systematic sequence, in which ECG leads are consecutively synthesized. A scanning step is the distance between consecutively synthesized ECG leads. A scanning sector is a part of the three-dimensional space that is selected for ECG scanning. A scanning time is the moment of a cardiac cycle that is selected for synthesizing ECG leads. A scanning period is the time period that is selected for synthesizing ECG leads. A scanning rate is the frequency that is selected for synthesizing ECG leads during a scanning period.
In a preferred embodiment, an ECG scanner utilizes the eight active channels of the conventional 12-lead electrocardiography as original leads to systematically synthesize ECG leads having arbitrary positions. A pair of dihedral angles xcex1 and xcex2 (independent variables) of the global coordinate system determines the position of a synthesized lead. The shares of the eight channels in a newly synthesized ECG lead are equal to the products of the respective (i) shares of the eight channels in the three orthogonal leads X, Y, Z and (ii) shares of the three orthogonal leads in a synthesized lead. Shares of the eight channels in the three orthogonal leads (constants) are published. Shares of the three orthogonal leads in a newly synthesized lead are calculated by a means for calculating shares using the following formulae (functions):
share of X=cos xcex1xc3x97cos xcex2
share of Y=sin xcex1xc3x97cos xcex2
share of Z=cos xcex1xc3x97sin xcex2.
An ECG scanner includes a means for automatically analyzing synchronous electric signals of ECG leads, which includes a means for measuring synchronous electric signals of ECG leads; a means for comparing measurements; and a means for selecting measurements that meet predetermined criteria (extremeness of measured values, normal range, accepted diagnostic criteria, etc.).
An ECG scanner includes a means for visualizing electric signals of synthesized ECG leads. A synthesized ECG lead where pathological signs are mostly manifesting can be selected for continuous ECG monitoring. ECG scanning can be conducted in a patient during a stress test.
In order to make ECG scanning more accurate and reproducible, an ECG scanner includes a means for adjusting for a particular patient shares of original leads in synthesized leads, which results in minimum dissimilarity between homologous original and synthesized leads. In a preferred embodiment, a means for adjusting automatically adjusts shares of the eight active channels of the standard 12-lead electrocardiography in the three orthogonal leads. Thus adjusted shares are subsequently used for ECG scanning in that patient.
Knowing the position of a synthesized ECG lead is paramount for ECG scanning. For that purpose, a means for computing positions of synthesized leads is disclosed. In a preferred embodiment, automated ECG scanning is accompanied by building a three-dimensional image of a scanning lead, which is easy to comprehend.
A cardiac imaging system for non-invasively visualizing electric processes in the heart by matching heart structures of a patient with electric signals originating therefrom is disclosed.
Information on ECG scanning can be recorded by an appropriate means onto a suitable carrier for an off-line analysis, data interchange, storage, documentation, and other purposes.
In a preferred embodiment, an ECG scanner automatically scans the three-dimensional space formed of a boundless number of synthesized ECG leads to detect the one which is collinear with a pathology and where earlier invisible or poorly discernible pathological ECG signs become noticeable or more manifesting and reaching diagnostic thresholds. An ECG scanner can operate in a background mode while a routine ECG is taken, and show itself only when a pathological sign is automatically detected. ECG scanning can substitute for or enhance the standard 12-lead ECG and VCG, and effectively supplement any cardiac investigation. ECG scanning is easy to use, does not require much extra training for physicians, and is relatively inexpensive.